A Private Land Mobile Radio (PLMR) system is a Push to Talk (PTT) Point to Multipoint (PtMP) wireless communication system operating below 1 GHz. PLMR systems are primarily used for voice communication between groups of users. Only one user of the group can talk at any one time by pressing the button (i.e., activating PTT) while the rest of the users in the group are listening.
PLMR networks have evolved as voice centric systems making it difficult to support emerging mission critical data applications, such as remote data base access, for example. PLMR systems have several drawbacks, as follows:
Firstly, communication in PLMR systems is generally over narrowband PLMR channels. A PLMR channel width of 25 KHz has been typically used, but FCC regulations have mandated the narrow banding of certain frequencies, reducing channel sizes from 25 KHz to 12.5 KHz in order to double the number of available PLMR channels. The FCC is considering a further decrease in PLMR channel width to 6.25 KHz. As a result, while PLMR channels can support excellent voice quality, data communication is very slow.
Secondly, most PLMR systems are circuit switched systems. As such, they are not efficient for data communication. Research with real customer data reveals that channel voice occupancy is typically very low.
Several solutions have been proposed for PLMR systems to deliver data services, as follows:                Public wireless networks: These networks typically lack coverage across the PLMR user's serving area. Also, with their commitment to serve the general public, these systems are not considered mission critical by the PLMR users.        Dedicated data networks operating in unlicensed bands (900 MHz, 2.4 GHz or 5.8 GHz). Because of transmit power restrictions in the unlicensed bands as well as the higher frequency (relative to the PLMR operating frequencies); the coverage of these systems is relatively poor. Coverage can be improved with a costly dense node deployment. In addition, these systems are not considered robust enough for mission critical applications and are limited in their support of mobility.        Dedicated data networks operating in a licensed band (e.g. 700 MHz): Though this solution supports mission critical high speed data, it is very costly since the operator needs to pay for both the licensed frequencies and the new infrastructure.        
Prior art solutions include U.S. Pat. No. 5,491,837 to Haartsen, which describes a method and system for channel allocation using power control and mobile-assisted handover measurements. US Patent Application No: 20070072554 to Janky describes a system and method for automatic roaming for conventional land mobile radios (LMR). U.S. Pat. No. 5,157,709 to Ohteru describes a Radio communications system adaptively assigning channels using power levels of idle channels. U.S. Pat. No. 4,144,496 to Cunningham describes a Mobile communication system and method employing frequency reuse within a geographical service area. U.S. Pat. No. 6,611,536 to Ahmed describes a System and method for integrating voice and data on a single RF channel.
None of the prior art documents describe the feature of a base station maintaining a two-way data communication with mobile remote radios in its service area over idle PLMR channels.
There is thus a need to provide an innovative wireless system and a method to implement a mission critical high speed data solution with similar coverage to the existing voice service, which overcome the disadvantages of present systems.